• Geophysics and Geophysical Exploration
• /
• v.15 no.4
• /
• pp.235-244
• /
• 2012

Nuclear magnetic resonance (NMR) logging has been considered one of the most complicated nevertheless, one of the most powerful logging methods for the characterization on of both rocks and natural fluids in formation. NMR measures magnetized signals (polarization and relaxation) between the properties of hydrogen nucleus called magnetic moment and applied magnetic fields. The measured data set contains two important petrophysical properties such as density of hydrogen in the fluids inside the pore space and the distinct decay rate for fluid type. Therefore, after the proper data processing, key petrophysical information, not only the quantities and properties of fluids but also supplies of rock characterization in a porous medium, could be archived. Thus, based on this information, several ongoing researches are being developed in estimating aspects of reservoir productivity information, permeability and wettability since it is the key to having correct interpretation. This study goes through the basic theory of NMR at first, and then reviews NMR logging tools as well as their technical characteristics. This paper also briefly discusses the basic knowledge of NMR simulation algorithm by using Random walk.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.16 no.4
• /
• pp.465-472
• /
• 2013

Since 1990, Agency for Defense Development is operating the non-magnetic laboratory for the development of key technology for the underwater magnetic stealth part, the research of the magnetic application weapons and the technical support for Korean Navy. Recently, we installed the new three-axis earth magnetic field simulator and the measurement system in the non-magnetic laboratory which is replacing the existing outdated facility. In this paper, we deal with the detailed design result of the earth magnetic field simulator and the measurement system. Also, we describe the effective method to separate the permanent and the induced magnetic field from the measured data for a scaled model ship using the earth magnetic field simulator and the measurement system.

• The Journal of Engineering Geology
• /
• v.32 no.4
• /
• pp.611-625
• /
• 2022

One of the applications of geomagnetic paleo-secular variation (PSV) is the age dating of archeological remains (i.e., the archeomagnetic dating technique). This application requires the local model of PSV that reflects non-dipole fields with regional differences. Until now, the tentative Korean paleosecular variation (t-KPSV) calculated based on JPSV (SW Japanese PSV) has been applied as a reference curve for individual archeomagnetic directions in Korea. However, it is less reliable due to regional differences in the non-dipole magnetic field. Here, we present PSV curves for AD 1 to 600, corresponding to the Korean Three Kingdoms (including the Proto Three Kingdoms) Period, using the results of archeomagnetic studies in the Korean Peninsula and published research data. Then we compare our PSV with the global geomagnetic prediction model and t-KPSV. A total of 49 reliable archeomagnetic directional data from 16 regions were compiled for our PSV. In detail, each data showed statistical consistency (N > 6, 𝛼₉₅ < 7.8°, and k > 57.8) and had radiocarbon or archeological ages in the range of AD 1 to 600 years with less than ±200 years error range. The compiled PSV for the initial six centuries (KPSV0.6k) showed declination and inclination in the range of 341.7° to 20.1° and 43.5° to 60.3°, respectively. Compared to the t-KPSV, our curve revealed different variation patterns both in declination and inclination. On the other hand, KPSV0.6k and global geomagnetic prediction models (ARCH3K.1, CALS3K.4, and SED3K.1) revealed consistent variation trends during the first six centennials. In particular, the ARCH3K.1 showed the best fitting with our KPSV0.6k. These results indicate that contribution of the non-dipole field to Korea and Japan is quite different, despite their geographical proximity. Moreover, the compilation of archeomagnetic data from the Korea territory is essential to build a reliable PSV curve for an age dating tool. Lastly, we double-check the reliability of our KPSV0.6k by showing a good fitting of newly acquired age-controlled archeomagnetic data on our curve.

• Journal of the Korean Magnetics Society
• /
• v.24 no.1
• /
• pp.22-27
• /
• 2014

North indicating azimuth angle sensors have been used in airplanes, ships traditionally and nowadays employed in smart phones. For the azimuth and roll angle measurement of the sensor, 3-axis acceleration sensor was added to the 3-axis magnetic field sensor. In this work, we have constructed a measuring system for the measurement of the magnetic field and the angle uncertainty of the magnetic field sensors. Measuring system could be useful not only in non-magnetic laboratory but also in normal laboratory, we constructed small size of 3-axis Helmholtz coils for the compensation environment magnetic field (Earth magnetic field and magnetic field from building) and the generation of magnetic field for the test of magnetic field sensor. The constructed measuring system could compensate environment magnetic field below 10 nT level and generate 3-dimensional magnetic field with magnitude uncertainty of 0.2 % and angle error of $0.2^{\circ}$ within the volume of ${\pm}30mm$ diameter at center of Helmholtz coils. For the conformation of developed measuring system, We tested commercially available 3-axis magnetometer and heading sensor.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 2006.06b
• /
• pp.87-90
• /
• 2006

The Earth's spherical harmonic model of the main field and of the secular variation, of the geomagnetic field gives the intensity and geomagnetic structure at any location around the earth, assuming an undistorted, steady state field that no external sources or localized earth anamalies. To consider the practical use of a ship's digital compass in earth's magnetic field, Earth's spherical harmonic model is searched for the related practical methods and procedures as a basic study in this work.

• Journal of the Korean Magnetics Society
• /
• v.18 no.2
• /
• pp.54-57
• /
• 2008

Magnetic torquer, which uses torque between magnetic dipole moment and earth magnetic field, has been used to control attitude of satellites. In this work, we developed a magnetic torquer for small scientific satellite and test under environmental conditions of the satellite launching and orbital motion have been carried out. The developed magnetic torquer shows saturation magnetic dipole moment of $15Am^2$, linearity of 0.3 % in the range of ${\pm}12Am^2$, mass of 0.46 kg, and power consumption of 1 Watt at magnetic dipole moment of $10Am^2$.

• Geophysics and Geophysical Exploration
• /
• v.15 no.2
• /
• pp.66-74
• /
• 2012

This paper presents development of a three-dimensional marine controlled-source electromagnetic (mCSEM) modeling algorithm and its application to a salt and reservoir model to examine detectability of mCSEM for a reservoir under complex subsurface structures. The algorithm is based on the finite difference method, and employs the secondary field formulation for an accurate and fast calculation of modeling responses. The algorithm is verified for a two-layer model by comparing solutions not only with analytic solutions but also with those from other 3D modeling algorithm. We calculate and analyze electric and magnetic fields and their normalized responses for a salt and reservoir model due to three sources located at boundaries between a salt, a reservoir, and background. Numbers and positions of resistive anomalies are informed by normalized responses for three sources, and types of resistive anomalies can be informed when there is a priori information about a salt by seismic exploration.

• Geophysics and Geophysical Exploration
• /
• v.14 no.2
• /
• pp.164-175
• /
• 2011

Using natural electromagnetic (EM) fields at low frequencies, magnetotelluric (MT) surveys can investigate conductivity structures of the deep subsurface and thus are used to explore geothermal energy resources and investigate proper sites for not only geological $CO_2$ sequestration but also enhanced geothermal system (EGS). Moreover, marine MT data can be used for better interpretation of marine controlled-source EM data. In the interpretation of MT data, MT modeling schemes are important. This study improves a three dimensional (3D) MT modeling algorithm which uses edge finite elements. The algorithm computes magnetic fields by solving an integral form of Faraday's law of induction based on a finite difference (FD) strategy. However, the FD strategy limits the algorithm in computing vertical magnetic fields for a topographic model. The improved algorithm solves the differential form of Faraday's law of induction by making derivatives of electric fields, which are represented as a sum of basis functions multiplied by corresponding weightings. In numerical tests, vertical magnetic fields for topographic models using the improved algorithm overcome the limitation of the old algorithm. This study recomputes induction vectors and tippers for a 3D hill and valley model which were used for computation of the responses using the old algorithm.

• Journal of the Korean earth science society
• /
• v.30 no.6
• /
• pp.692-698
• /
• 2009

Wavelet transform has been widely used in terms that it may overcome the shortcoming of conventional Fourier transform. Fourier transform has its difficulty to explain how the transformed domain, frequency, is related with time. Traditional semblance technique in Fourier transform was devised to compare two time series on the basis of their phase as a function of frequency. But this method is known not to work well for the non-stationary signal. In this study, we present two applications of the wavelet-based semblance method to geophysical data. Firstly, we show filtered geomagnetic signal remained with components of high correlation to each observatory. Secondly, highly correlated residual signal of gravity and magnetic survey data, which are also filtered by this semblance method, is present.

• Journal of the Korean earth science society
• /
• v.25 no.7
• /
• pp.604-614
• /
• 2004

Using three-components geomagnetic data from a permanent geomagnetic observatory in Icheon, we have computed the power spectrum of each geomagnetic component, amplitude, phase and estimation error of transfer function for each day in the 6 months period July 2002${\sim}$December 2002. The temporal variation of power spectrum have random appearances with repeating relative strong and weak magnitude, which is considered as solar activities. However, there is no clear long-term trend. In the case of amplitude, phase and error of transfer function, even though there are some random patterns over the periods of 1000 s and under 100 s, they seem to be comparatively stable without manifest temporal changes. Futhermore, we have estimated electrical field by assuming P$_{1}\;^{0}$ spherical harmonics and then calculated the approximated apparent resistivity for each day. As a result, the variations of resistivity depend on the temporal magnitude of spectral power in horizontal magnetic fields rather than hydrological changes in near surface.